The present invention relates generally to distance measuring devices and more particularly to a non-contacting optical device for measuring the inner diameter and inner cross sectional profile of a tube.
There are many ways to measure distance, both by direct contact, and optically. However, there has not heretofore been a completely satisfactory method of measuring the inner diameter and/or the entire inner cross sectional profile or configuration of a tube.
As will be seen hereinafter, the present invention combines fiber optics with an array of photocells, particularly light sensitive diodes in a preferred embodiment, to provide an uncomplicated and economical distance measuring device and yet one which is reliable in use. This particular device is especially suitable for detecting dents in the secondary lines of a steam generator. "Denting" is the term used to describe the results of a corrosion process that occurs on the secondary side of the generator. Corrosion products, principally non- protective magnetite, builds up in the gap (crevice region) between the outer diameter surface and the surface of the carbon steel support plate comprising part of the generator's secondary side. With time, the thickness of this deposit grows and compresses or dents the tube, in the tube support plate region. During the initial stages of compression, the internal diameter is believed to decrease uniformly. However, at some point, this uniform decrease in internal configuration assumes an oval contour. More recently, some evidence has indicated that ovalization is followed by a tube contour assuming a kidney bean shape. Because of the diametrical changes associated with this progression of denting, it is valuable to have a device that traverses the inner diameter of the tube and makes sufficient diametrical measurements to indicate the extent of denting. As will be seen hereinafter, the distance measuring device constructed in accordance with the present invention is particularly suitable for this type of application.